In the line of what everyone has been saying, I'd suggest diesel-powered "Professional Versions" for the entire lineup. They do it in Europe, why shouldn't they do it in the US?
I am sure that more than one taxi fleet will be glad to put a few Mercedes to the task!

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[GONE] - 1995 Mercedes E300 Diesel - 130k miles - Smoke Silver (702) over Mushroom leather (265) - Bladder blasting, coast-to-coast work machine.